There is a "pecking order" of these things. You can continue to try wood ashes and such or you can do pyrethrins, etc which many folks believe are less severe than Sevin and fairly effective. Worth a try, but you may end having to use Sevin.

When using the ashes, consider mixing in fine sand and clay. That may make so dust actually gets to where parasites are as bird baths. Otherwise ashes may not penetrate feathers as needed. My guess static charges of ash particles and feathers interact.